Abstract Immediate characterization of the effects of non-pharmaceutical interventions (NPIs) on community SARS/COV2 spread will be essential to safely re-opening the U.S. economy. We propose integration of rapid serologic assessment and extension of follow-up in an existing national cohort study of SARS/COV2, the CHASING COVID Cohort (C3) study. Launched on March 28th, 2020, we have already enrolled >4,700 adult participants from all 50 U.S. states and Puerto Rico into longitudinal follow-up (Figure), providing the opportunity for rapid investigation of the effect of different NPIs on SARS/COV2 spread in the United States. With this new application for funding, we seek to expand on this work by adding rapid serologic testing and extending follow-up to address the following specific aims: 1. Estimate the cumulative incidence of SARS/COV2, and evaluate impact of different NPIs on the cumulative incidence of SARS/COV2 infection, COVID (disease), and COVID deaths; 2. Estimate the proportion of persons with serologic evidence of SARS/COV2 infection who were asymptomatic or had only mild symptoms; 3. Assess whether SARS/COV2 antibodies are protective against subsequent COVID disease. We will conduct in-depth interviews with participants to help contextualize and interpret key findings. To help increase the scientific impact of this project, we will post public use datasets on GitHub, along with software tools. By deploying specimen collection now, the rapid knowledge gained by addressing the above aims will help inform policy and implementation and relaxing of NPIs, as well as mathematical models, in the US and around the world.